Comparative studies of SIMS and SNMS analyses during the build up of sputter equilibrium under oxygen and rare gas ion bombardment

Sputtering of solid surfaces by using a focused ion beam is the basis for secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS). The ion bombardment initiates not only redistribution of sample atoms but also massive changes in the surface and near surface composition of the bombarded area due to the sputter process and implantation of the primary ions. Changes in the matrix-composition affects the secondary ion yields and therefore a steady state (sputter equilibrium) has to be reached before SIMS data can give quantifiable results. SNMS is much less affected by those yield effects and therefore a combination of SIMS and SNMS can establish a basis for interpretation of SIMS data before the steady state is reached. In order to determine the effects of primary ion incorporation, we applied different primary ion species successively to generate different equilibria. An oxygen ion beam oxidizes the sample surface and by using a rare gas primary ion (PI) this oxide can be removed and analyzed.     

Depth profile analysis of thin film solar cells using SNMS and SIMS

SNMS (sputtered neutrals mass spectrometry) and SIMS (secondary ion mass spectrometry) are used for the depth profile analysis of thin film solar cells based on amorphous silicon. In order to enhance depth resolution, model systems are analyzed only representing parts of the layered system. Results concerning the TCO (transparent conducting oxide)/p interface and the n/i interface are presented. To minimize matrix effects, SNMS is used when the sample consists of layers with different matrices. Examples are the TCO/p interface (where the transition lengths of the depth profiles are found to be sharper when ZnO is used as TCO compared to SnO₂) and SnO₂/ZnO interfaces in coated TCO layers (where a Sn contamination inside the ZnO layer is found depending on the plasma pressure during the ZnO deposition). SIMS is used when the limits of detection reached by SNMS are not sufficient. Examples are H depth profiles in ZnO layers or P depth profiles near the n/i-interface.     

Quantitative Surface Analysis of a Binary Drug Mixture—Suppression Effects in the Detection of Sputtered Ions and Post-Ionized Neutrals

A systematic mass spectrometric study of two of the most common analgesic drugs, paracetamol and ibuprofen, is reported. The drugs were studied by means of secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS) using laser post-ionization (LPI) both in pure samples and in a two-component mixture. Ion suppression within the two-component system observed in SIMS mode is ameliorated using LPI under room temperature analysis. However, suppression effects are apparent in LPI mode on performing the analysis at cryogenic temperatures, which we attribute to changes in the desorption characteristics of sputtered molecules, which influences the subsequent post-ionization efficiency. This suggests different mechanisms of ion suppression in SIMS and LPI modes.

Comparative studies of MCs+-SIMS and e–-beam SNMS for quantitative analysis of bulk materials and layered structures

For the quantification of heterostructure depth profiles the knowledge of relative sensitivity factors (RSF) and the influence of matrix effects on the measured profiles is necessary. Matrix dependencies of the measured ion intensities have been investigated for sputtered neutral mass spectrometry (SNMS) and MCs(+)-SIMS. The use of Cs as primary ions for SNMS is advantageous compared to Ar because the depth resolution is improved without changing RSFs determined under Ar bombardment. No significant amount of molecules has been found in the SNMS spectra under Cs bombardment. Using MCs(+)-SIMS the RSFs are matrix dependent. An improvement of depth resolution can be achieved by biasing the sample against the primary ion beam for SNMS due to a reduction of the net energy of the primary ions and a resulting more gracing impact angle.     

Comparative studies of MCs+-SIMS and e?-beam SNMS for quantitative analysis of bulk materials and layered structures

For the quantification of heterostructure depth profiles the knowledge of relative sensitivity factors (RSF) and the influence of matrix effects on the measured profiles is necessary. Matrix dependencies of the measured ion intensities have been investigated for sputtered neutral mass spectrometry (SNMS) and MCs⁺-SIMS. The use of Cs as primary ions for SNMS is advantageous compared to Ar because the depth resolution is improved without changing RSFs determined under Ar bombardment. No significant amount of molecules has been found in the SNMS spectra under Cs bombardment. Using MCs⁺-SIMS the RSFs are matrix dependent. An improvement of depth resolution can be achieved by biasing the sample against the primary ion beam for SNMS due to a reduction of the net energy of the primary ions and a resulting more gracing impact angle.     

A simple erosion dynamics model of molecular sputter depth profiling

A simple model which describes the essential features commonly observed in a molecular sputter depth profile is presented. General predictions of the dependence of measured molecular ion signals on the primary ion fluence are derived for the specific case where a mass spectrometric technique such as SIMS or secondary neutral mass spectrometry (SNMS) is used to analyze the momentary surface. The results are compared with recent experimental data on molecular depth profiles obtained by cluster‐ion‐initiated SIMS of organic overlayers. Copyright © 2008 John Wiley & Sons, Ltd.     

Imaging of atomic and molecular species in tissue with laser‐SNMS for pharmaceutical studies

Successful anticancer therapies will have the ability to selectively deliver compounds to target cells while sparing normal tissue. Currently, methods to determine the distribution of compounds with very high sensitivity and subcellular resolution are still unavailable. Laser secondary neutral mass spectrometry (laser‐SNMS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) are capable of detecting atoms and molecules with high sensitivity and a spatial resolution of up to 80 nm. The use of such methods requires special preparation techniques that preserve the morphological and chemical integrity of living cells. In this paper, the ability of laser‐SNMS to study transportation processes in animals of boron‐containing compounds for boron neutron capture therapy will be discussed. The data show that with laser‐SNMS it is possible to measure the distribution of these compounds in tissues with subcellular resolution, and that laser‐SNMS is a very powerful tool for locating anticancer drugs in tissues. Copyright © 2006 John Wiley & Sons, Ltd.     

Operation and application of a new time-of-flight e-gas secondary neutral mass spectrometer (ToF–SNMS)

The low-pressure rf plasma of a secondary neutral mass spectrometer (e-gas SNMS) was connected with a time-of-flight (ToF) mass spectrometer for the first time. As opposed to ToF–SIMS in e-gas SNMS, the primary ion pulse cannot be used for triggering the flight time measurement. Therefore, an extraction pulse is used which at a defined time loads an ion package from the beam of the post-ionised particles into the ToF spectrometer. The newly developed ToF–SNMS system is described, and first experimental results are presented.     

Atom probe mass spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O₂⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.     

Multilayer thin-film coatings based on chromium nitride and aluminum nitride: Comparative depth profiling by secondary ion mass spectrometry and glow-discharge optical emission spectrometry

Round-robin characterization is reported on the sputter depth profiling of CrN/AlN multilayer thin-film coatings on nickel alloy by secondary ion mass spectrometry (SIMS) and glow-discharge optical emission spectrometry (GD-OES). It is demonstrated that a CAMECA SIMS 4550 Depth Profiler operated with 3 keV O ₂ ⁺ primary ions provides the best depth resolution and sensitivity. The key factor is sample rotation, which suppresses the negative influence of the surface topography (initial and ion-induced) on the depth profile characteristics.     

Multielement ultratrace analysis in tungsten using secondary ion mass spectrometry

Summary The ever increasing demands on properties of materials creates a trend also towards ultrapure products. Characterization of these materials is only possible with modern, highly sophisticated analytical techniques such as activation analysis and mass spectrometry, particularly SSMS, SIMS and GDMS [1].Analytical strategies were developed for the determination of about 40 elements in a tungsten matrix with high-performance SIMS. Difficulties like the elimination of interferences had to be overcome. Extrapolated detection limits were established in the range of pg/g (alkali metals, halides) to ng/g (e. g., Ta, Th).Depth profiling and ion imaging gave additional information about the lateral and the depth distribution of the elements.

---

Multielementepurenanalyse in Wolfram mittels SIMS

     

Quantitative depth profiling of argon in tungsten films by secondary ion mass spectrometry.

Depth profiling of Ar in Ar-implanted tungsten (W) films with an excellent detection limit was investigated by secondary ion mass spectrometry (SIMS). Depth profiles of Ar with the detection of Ar+ and ArCs+ secondary ions, which were produced by O2+ and Cs+ primary ions, respectively, were compared in view of the detection limit and the depth resolution. The detection limit of Ar monitoring Ar+ was limited by the carbon- and oxygen-containing molecular ion (C2O+) in the sample as well as in the SIMS instrument. It was observed that some of the Ar+ ions were produced in the vacuum above the sample surfaces, whereas the ionization of almost all C2O+ occurred at the samples. By using different energy spectra between Ar+ and C2O+, we showed that the energy-filtering technique is advantageous for suppressing C2O+ ion detection. It is also confirmed that the ArCs+ secondary ion is only slighting by the C2OCs+ mass-interference ion. A detection limit of 4 x 10(18) cm(-3) for monitoring Ar+ and 3 x 10(16) cm(-3) for monitoring ArCs+ was achieved under a primary-ion current density of 0.16 mA/cm2. The detection of ArCs+ ion rather than Ar+ was found to be superior in the detection limit and the depth resolution. We conclude that SIMS is useful for the determination of the Ar depth distribution in W films.     

XRF and SIMS/SNMS analyses of Ba<Subscript>x</Subscript>Sr<Subscript>1−x</Subscript>TiO<Subscript>3</Subscript> dielectrics

The development of analytical tools and procedures for process control is a prerequisite for the integration of high permittivity and/or ferroelectric materials in CMOS devices. The thickness and composition of perovskite oxide films were determined by wavelength dispersive X-ray fluorescence analysis (XRF) with special emphasis on the ratio of the group-II elements to the Ti content, and a precision of 0.5% was achieved for a typical film thickness of 20-30 nm. Secondary ion mass spectrometry (SIMS) and sputtered neutrals mass spectrometry (SNMS) was used for depth profiling to determine film homogeneity and elemental interdiffusion at hetero-interfaces. Examples are given for Ba(x)Sr(1-x)TiO(3) and SrTiO(x) thin films which were grown in a prototype MOCVD production tool. No interdiffusion was observed for films grown at 600 degrees C on Pt electrodes in contrast to films grown directly on Si.     

TOF‐SIMS matrix effects in mixed organic layers in Ar cluster ion depth profiles

Matrix effects are crucial for analyses using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) in terms of quantitative analysis, depth profiling and imaging. It is often difficult to predict how co‐existing materials will influence each other before such analysis. However, matrix effects need to be curtailed in order to assume the appropriate amount of a target material in a sample. First, matrix effects on different types of organic mixed samples, including a sample composed of Irganox 1010 and Irganox 1098 (MMK sample) and another composed of Irganox 1010 and Fmoc‐pentafluoro‐L‐phenylalanine (MMF sample), were observed utilizing ToF‐SIMS and the dependence of the secondary ion polarity of the matrix effects on the same sample was evaluated. Next, the correction method for the ToF‐SIMS matrix effects proposed by Shard et al. was applied to a comparison of the positive secondary ion results to the negative ones. The matrix effects on the positive ion data in both samples were different from those on the negative ion data. The matrix effect correction method worked effectively on both the negative and positive depth profiles. Copyright © 2017 John Wiley & Sons, Ltd.     

Mass spectrometric analysis of ceramic components for solid oxide fuel cells

For the determination of trace impurities in ceramic components of solid oxide fuel cells (SOFCs), some mass spectrometric methods have been applied such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). Due to a lack of suitable standard reference materials for quantifying of analytical results on La _x Sr _y MnO₃ cathode material a matrix-matched synthetic standard-high purity initial compounds doped with trace elements-was prepared in order to determine the relative sensitivity coefficients in SSMS and LA-ICP-MS. Radiofrequency glow discharge mass spectrometry (rf-GDMS) was developed for trace analysis and depth profiling of thick non-conducting layers. Surface analytical techniques, such as secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS), were used to determine the element distribution on surfaces (homogeneity) and the surface contaminants of SOFC ceramic layers.Dedicated to Professor Dr. rer. nat. Hubertus Nickel on the occasion of his 65th birthday     

The analysis of industrial synthetic polymers by electrospray droplet impact/secondary ion mass spectrometry

Electrospray droplet impact (EDI)/secondary ion mass spectrometry (SIMS) is a new desorption/ionization technique for mass spectrometry in which highly charged water clusters produced from the atmospheric‐pressure electrospray are accelerated in vacuum by several kV and impact the sample deposited on the metal substrate. In this study, several industrial synthetic polymers, e.g. polystyrene (PS) and polyethylene glycol (PEG) were analyzed by EDI/SIMS mass spectrometry. For higher molecular weight analytes, e.g. PS4000 and PEG4600, EDI/SIMS mass spectra could be obtained when cationization salts are added. For the polymers of lower molecular weights, e.g. PEG300 and PEG600, they could be readily detected as protonated ions without the addition of cationization agents. Anionized PS was also observed in the negative ion mode of operation when acetic acid was added to the charged droplet. Compared to matrix‐assisted laser desorption/ionization (MALDI), ion signal distribution with lower background signals could be obtained particularly for the low‐molecular weight polymers. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct profiling of saccharides,organic acids and anthocyanins in fruits using electrospray droplet impact/secondary ion mass spectrometry

Electrospray droplet impact (EDI)/secondary ion mass spectrometry (SIMS) is a new desorption/ionization technique for mass spectrometry in which highly charged water clusters produced from atmospheric‐pressure electrospray are accelerated in vacuum by several kV and impact on the sample deposited on the metal substrate. In this study, we applied EDI/SIMS directly to fruits, such as bananas, strawberries, grapes and apples. The major components in the fruits – fructose, glucose, sucrose and organic acids – could be observed with strong signal intensities. EDI/SIMS was also applied to the analysis of different regions of strawberries and apples. Compared with matrix‐assisted laser desorption/ionization (MALDI), ion signals with lower background signals could be obtained, particularly for the low molecular weight analytes. Copyright © 2010 John Wiley & Sons, Ltd.     

Matrix‐enhanced secondary ion mass spectrometry: the influence of MALDI matrices on molecular ion yields of thin organic films

In this work the effect in secondary ion mass spectrometry (SIMS) of several frequently used matrix‐assisted laser desorption/ionisation (MALDI) matrices on the secondary ion intensities of low molecular weight (m/z 400–800) organic dyes and a pharmaceutical is tested. Matrix (10^?1 M) and analyte (10^?2 M) solutions were made in methanol. Mixtures with several concentration ratios were prepared from these solutions and spincoated on Si substrates prior to time‐of‐flight (TOF)‐SIMS analysis. In some cases the presence of the MALDI matrices caused a considerable increase in the positive secondary (protonated) molecular ion signals. Enhancements of a factor of 20 and more were recorded. Generally, of the matrices used, 2,5‐dihydroxybenzoic acid and 2,4,6‐trihydroxyacetophenone brought about the highest intensity increases. It was also shown that matrix‐enhanced (ME‐)SIMS is capable of lowering the detection limits for molecule ions. However, the enhancement effect is strongly influenced by the analyte/matrix combination and its concentration ratio. As a result, finding an optimal analyte/matrix mixture can be a very time‐consuming process. Mostly, the presence of the matrices causes changes in the relative ion intensities in the TOF‐S‐SIMS spectra. Compared to the spectra recorded from samples without matrices, only a few additional peaks, such as signals that originate directly from the applied matrix or adduct ions, are observed in the mass spectra. Sometimes molecule ions and some characteristic fragments at high m/z values, that cannot be recorded without matrix, do appear in the spectrum when a matrix is present. In the negative mode no enhancement effect is observed on applying the studied MALDI matrices. The results obtained from samples treated with MALDI matrices are also compared to SIMS results for the same samples after Ag and Au metallisation (MetA‐SIMS). For three of the four tested compounds Au MetA‐SIMS resulted in higher ion yields than ME‐SIMS. For both techniques possible mechanisms that can account for the enhancement effect are proposed. Copyright © 2005 John Wiley & Sons, Ltd.     

A particulate isotopic standard of uranium and plutonium in an aluminosilicate matrix

Mixed-actinide microstandard particles have been produced for calibration and performance testing of isotope-ratio mass spectrometers and ion and electron microprobe instruments. The spherical micrometer-size particles consist of an aluminosilicate matrix loaded with 2.2% by weight of isotopically certified uranium and 0.11% by weight of isotopically certified plutonium. The uranium and plutonium isotopic compositions have been verified by both thermal ionization mass spectrometry and secondary ionization mass spectrometry (SIMS). The elemental composition of the microspheres has been determined by both electron microprobe and SIMS analysis.     

Identifying and minimizing buffer interferences in ToF‐SIMS analyses of lignocellulose

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has demonstrated applicability to the analysis of lignocellulosic samples including pulp, paper, plants, and wood. One such application is to use ToF‐SIMS as a tool for detecting the activity of enzymes applied to degrade or modify plant biomass. The use of buffers for pH control of these enzymatic reactions can pose problems due to the nature of the ToF‐SIMS measurement. Specifically, inorganic species (e.g. salts) from buffer components could introduce several concerns for quantitative or semi‐quantitative ToF‐SIMS analysis. First, salts can produce additional peaks in the mass spectra, which may overlap with lignocellulose peaks of interest (mass interference). Second, salts can alter the chemical environment, or ‘matrix’, altering the ionization probability of lignocellulose‐related secondary ions during the sputtering mechanism of the ToF‐SIMS measurement (matrix effects). Third, salts may physically coat the lignocellulose surface, decreasing the signal from the lignocellulose, causing poor signal‐to‐noise in the analysis. The current work presents a simple approach for identifying interferences due to buffers, using both principal component analysis (PCA) and previously established lignocellulose‐relevant peak ratios. Furthermore, a simple acetic acid rinsing protocol is compared to distilled water rinsing and is evaluated and for its effectiveness in removing buffer‐related salts. The data shows that briefly rinsing lignocellulose samples in dilute acetic acid can be effective in restoring the validity of lignocellulose composition interpretations using ToF‐SIMS. Copyright © 2014 John Wiley & Sons, Ltd.